By Onche Odeh
A new survey conducted by the Nigeria Centre for Disease Control (NCDC) in collaboration with the Nigeria Institute for Medical Research (NIMR) and partners has revealed that as many as 1 in 5 individuals in three Nigerian states of Lagos, Enugu and Nasarawa State would have ever been infected with Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) virus, the virus that causes COVID-19.
The seroprevalence surveys of household conducted in Lagos, Enugu, Nasarawa and Gombe released this week show a similar trend in Gombe, where the rate of infection with SARS-CoV-2 is estimated at 1 in 10 persons.
Further findings from the survey that was conducted between September and October 2020 show that the rates of COVID-19 infection among people in the states are higher than those reported through the national surveillance system.
This, according to a statement jointly signed by NCDC’s Director General, Dr. Chikwe Ihekweazu and his NIMR counterpart, Professor Babatunde Salako, reveals also that the spread of infection in the states surveyed is wider than is obvious from surveillance activities.
The statement noted that this is not surprising for COVID-19, given that most of those infected do not have any symptoms.
The surveys were designed to improve the estimate of the burden of COVID-19 infection in the country and provide a more detailed estimate of the extent of infection with SARS-CoV-2.
Blood samples for this survey were collected from over 10,000 individuals residing in a representative sample of households in the four states. The blood samples were then tested for the presence of SARS-CoV-2 antibodies applying locally validated laboratory tests. Individuals who provided blood samples also answered a brief questionnaire that enabled the study team to characterise factors related to positivity and identify which population groups were most affected.
Findings from the study revealed that the prevalence of SARS-CoV-2 antibodies was 23% in Lagos and Enugu States, 19% in Nasarawa State, and 9% in Gombe State. This means that as many as 1 in 5 individuals in Lagos, Enugu and Nasarawa State would have ever been infected with SARS-CoV-2. In Gombe, the proportion is about 1 in 10.
Results of the survey further showed higher rates of infection among: 1) males than females (for example, 10% vs. 7% in Gombe and 21% vs. 17% in Nasarawa); 2) urban compared to rural and residents (for example, 28% vs. 18% in Enugu and 23% vs. 19% in Lagos); and persons aged 18-64 years. There were also variations across the local government areas (LGA) within the four states. The survey team noted that these observations are in tandem with what had been reported by the NCDC based on the national surveillance system.
In interpreting the results, the survey team stated that “SARS-CoV-2 emerged only one year ago and antibody response according to severity of infection and the duration of antibody persistence are not yet completely understood”.
Given the high proportion of asymptomatic cases in Nigeria, the true seroprevalence of ever having infection may be underestimated in the survey if individuals infected early in the outbreak no longer had sufficient antibodies for detection when the survey was conducted, the statement pointed out.
“The results from the survey show that a significant proportion of people in Nigeria are still at risk of SARS-CoV-2 infection and therefore, COVID-19. It is very important that Nigerians continue to adhere to public health and social measures including regular handwashing, proper use of face masks and physical distancing,” the statement noted.
The survey supported by the United States Centers for Disease Control and Prevention (US-CDC), the University College London (supported by Bill and Melinda Gates Foundation), the University of Maryland, Baltimore (UMB) and the respective State Ministries of Health is being expanded to more states with a priority to capture information from States in the North-West and South-South geopolitical zones which were not included in the initial round of surveys.